This invention concerns a color cathode ray tube with a shadow mask.
Color cathode ray tubes are used for displays for terminal monitors and TV receivers, etc. Generally, a color cathode ray tube includes the following components:
(1) Vacuum envelope made of the glass including a panel portion, a neck portion, and a funnel portion.
(2) Fluorescent screen formed in the inner surface of the face plate of the panel portion.
(3) Shadow mask that faces the fluorescent screen inside of the panel portion.
(4) Electron gun in the neck portion.
(5) Deflection yoke fixed in the circumference of the funnel portion.
With large number of dots state electron beam passage holes, the shadow mask contains a rectangle porous portion with a fixed curved surface, a nonporous rectangle frame portion with a whole circumference porous edge portion and an equal curved surface with the porous portion, and bent skirt portion which trails from all the peripheral of the nonporous portion. By pressing and shaping the metallic material for the shadow mask composition, the porous portion, nonporous portion and skirt portion are united.
The inventors have found that an elongation of the diameter of the dot state electron beam passage holes increases in the marginal region of porous portion in comparison with center region of porous portions, when the shadow mask was composed unitedly by the press shaping. That is to say, dot transformability which is applied in the dot state electron beam passage hole is bigger in marginal region of porous portion than in center region of porous portion, due to the press shaping. Therefore, the diameter of dot state electron beam passage holes greatly increases by applying large transformability in each corner region especially in the marginal region of porous portion in comparison with center region of porous portion.
In the display monitor for an information processing terminal such as the computer, there tends to be a year by year increase of the display image high resolution. In color cathode ray tube for such display monitor, high-definition of the phosphor pixel (dot) which constitutes the fluorescent screen is required. That is to say, it is necessary to make the interval (pitch) of the phosphor dot small. Like this, it is necessary to make the interval (pitch) in the electron beam passage hole of the dot state of the shadow mask small in order to provide a fluorescent screen of color cathode ray tube of high-definition.
Electron beam cross-sectional shape expands especially in the corner region of the peripheral region of the fluorescent screen of the color cathode ray tube, when the shadow mask in which the diameter of the aforesaid dot state electron beam passage hole increases was used in color cathode ray tube of such high-definite screen. The phenomenon which also irradiates not only the fluorescent body which should originally shine but also adjoining fluorescent body arises by this. By reducing the interval (pitch) of electron beam passage holes in the shadow mask and the interval (pitch) of phosphor dot in the fluorescent screen, this is as the electron beam becomes easy to reach to adjacency fluorescence body dot. Landing tolerance of the electron beam lowers, and the color purity of the image displayed in color cathode ray tube deteriorates, and it is not possible to display the high-quality image.
Since it was not needed to reduce the interval (pitch) of phosphor dot and shadow mask electron beam passage holes without requiring high-definition of fluorescent screen in color cathode ray tube for the public TV receiver, landing tolerance lowering of the superscription electron beam was not doubted.
An object of the invention is to reduce the deformation of the dot state electron beam passage hole which is located in the corner region of the porous portion in the press shaping of the shadow mask to solve the aforesaid problem, and offer a shadow mask type color cathode ray tube which enables the display of the high-quality image.
The shadow mask type color cathode ray tube by this invention contains the following composition in order to achieve the aforesaid purpose.
The envelope equipped for shadow mask type color cathode ray tube of this invention includes panel portion with face plate, neck portion, and funnel portion which connects panel portion with neck portion.
The fluorescent screen equipped for shadow mask type color cathode ray tube of this invention is formed in the inner surface of face plate.
The electron gun equipped for shadow mask type color cathode ray tube of this invention is stored in neck portion.
The deflecting yoke equipped for shadow mask type color cathode ray tube of this invention is fixed in the circumference (the neck portion approach) of funnel portion.
The shadow mask equipped for shadow mask type color cathode ray tube of this invention is placed in order to face the inside of panel portion with fluorescent screen, and the original plate with porous portion of substantially rectangle state which established large number of electron beam passage holes is being pressed and is being shaped.
The diameter of the electron beam passage holes is smaller in the four corner regions than the center region of the porous portion.
Or, the width of the bridge which connects electron beam passage holes which adjoins for the oblique direction is bigger in four corner regions than the center region of porous portion.
And, shadow mask type color cathode ray tube by this invention may include following composition in order to achieve the aforesaid purpose.
(means 1A) In the shadow mask original plate before it is shaped, the diameter of the electron beam passage holes decreases by the power 1.5 of the distance of the direction which approaches the corner edge in a first range of substantially quadrangular state surrounded by a next four points from a reference point.
(1) Each corner edge of porous portion.
(2) Reference point which left several mm along the diagonal line in the central direction from the each corner edge of porous portion.
(3) Horizontal peripheral line edge of porous portion which is horizontally from reference point in reverse direction for the perpendicular center line of porous portion.
(4) Perpendicular peripheral line edge of porous portion which is perpendicular from reference point in reverse direction for the level center line of porous portion.
(means 1B) In the shadow mask, before pressing and shaping the original plate the width of the bridge increases by the power 1.5 of the distance of the direction which approaches the corner edge in the first range from the reference point.
And, shadow mask type color cathode ray tube by this invention may include following composition in order to achieve the aforesaid purpose.
(means 2A) In addition to aforesaid means 1A, the diameter of the electron beam passage hole proportionally increases in the second range of substantially quadrangular state surrounded by next 4 points in the second reference point direction from reference point side.
(1) Reference point of porous portion in shadow mask original plate.
(2) Second reference point which horizontally left several mm in approaching to the perpendicular center line of porous portion from reference point.
(3) Perpendicular peripheral line edge of porous portion which is perpendicularly from reference point in reverse direction for the level center line of porous portion.
(4) Second perpendicular peripheral line edge of porous portion which is perpendicularly from second reference point in reverse direction for the level center line of porous portion.
(means 2B) Or, the width of the bridge proportionally decreases in the second range in addition to aforesaid means 1B in the second reference point direction from the reference point side.
In addition, shadow mask type color cathode ray tube by this invention may include following composition in order to achieve the aforesaid purpose.
(means 3A) In addition to aforesaid means 1A, the diameter of the electron beam passage hole proportionally increases in the third range of substantially quadrangular state surrounded by next 4 points in the third reference point direction from reference point side.
(1) Reference point of porous portion in shadow mask original plate.
(2) Third reference point which perpendicularly left several mm in approaching to the level center line of porous portion from reference point.
(3) Horizontal peripheral line edge of porous portion which is horizontally from reference point in reverse direction for the perpendicular center line of porous portion.
(4) Second horizontal peripheral line edge of porous portion which is horizontally from third reference point in reverse direction for the perpendicular center line of porous portion.
(means 3B) Or, the width of the bridge proportionally decreases in the third range in addition to aforesaid means 1B in the third reference point direction from reference point side.
According to the aforesaid, substantially round shape dot state electron beam passage hole approaching the corner edge in the corner region of porous portion are of gradually reduced diameter. Or, there are gradually expanded bridge width portions approaching the corner edge. Therefore, the strength of the corner region of porous portion rises, as compared to the prior art, as it is close to the corner edge. As the result, the extension deformation of the aperture is suppressed, even if the considerably big transformability is applied in dot state electron beam passage holes in the corner region in composing the shadow mask unitedly by the press shaping. Then, it can be stopped that the diameter of each substantially round shape dot state electron beam passage hole expands in the corner region of the shadow mask. Electron beam cross section maintains the shape which is approximate to the substantially round shape, since the dot state electron beam passage hole is substantially circular in the corner region. Then, in a color cathode ray tube using such shadow mask, the landing tolerance of the electron beam is sufficiently ensured, and there is no degradation of the color purity of the image, and the high-quality image display can be carried out.